Schistosomiasis continues to be a major parasitic disease suffered by millions of people throughout the world. The underlying potentially lethal immunopathology in schistosomiasis is a granulomatous inflammation around parasite eggs, which is mediated by the host s T cells sensitized to parasite egg antigens. The proposed studies are based on the concept that such pathogenic T cell responses are amenable to down-regulation by immunotherapy, thereby resulting in the prevention of amelioration of disease. This approach has been referred to as anti-pathology vaccine. Specific T cell hybridomas will be used as probes to identify and isolate the major sensitizing egg antigens. Antigens will be cloned and their dominant T cell epitope peptide(s) will be synthesized. The type of elicited T cell response will be characterized and the genetic restriction of the T cell response will be determined. The major schistosomal egg antigen Sm-p40 will be the subject of close analysis by investigating the interaction of its dominant epitope 13mer peptide with the MHC class II molecule I-Ak, and by assessing its intrinsic pathogenicity. A broad range of experiments will test selected strategies involving specific homologous or altered peptides for the purpose of down-regulating the pathogenic T cell response. The long-term goal of this project is the achievement of effective and lasting specific T cell tolerance by way of a suitable biological vector capable of delivering the peptides into the host suffering from, or susceptible to, disease.